Otago Peninsula - Allans Beach Swell Statistics, Autumn: Surf with Light or Offshore Winds
This image shows only the swells directed at Otago Peninsula - Allans Beach that coincided with light winds or offshore conditions over a normal southern hemisphere autumn. It is based on 6580 predictions, one every 3 hours. The direction of the spokes show where quality surf generating swell comes from. Five colours represent increasing wave sizes. Very small swells of less than 0.5m (1.5 feet) high are shown in blue. Green and yellow show increasing swell sizes and red shows biggest swells greater than >3m (>10ft). In both graphs, the area of any colour is proportional to how commonly that size swell happens.
The diagram implies that the most common swell direction, shown by the longest spokes, was S, whereas the the prevailing wind blows from the NW. The chart at the bottom shows the same thing but without direction information. For example, swells larger than 1.5 feet (0.5m) coincided with good wind conditions 31% of the time, equivalent to 28 days. Open sea swells exceeding >3m (>10ft) are unlikely to arise in a normal southern hemisphere autumn but 2% of the time we expect swell in the range 2-3m (6.5-10ft) 2%, equivalent to (2 days). Taking into account the ratio of these swells that coincided with expected offshore winds, and given the fact that Otago Peninsula - Allans Beach is exposed to open water swells, we think that that clean surf can be found at Otago Peninsula - Allans Beach about 31% of the time and that surf is blown out by onshore wind 37% of the time. This is means that we expect 62 days with waves in a typical southern hemisphere autumn, of which 28 days should be clean enough to surf.
IMPORTANT: Beta version feature! Swell heights are open water values from NWW3. There is no attempt to model near-shore effects. Coastal wave heights will generally be less, especially if the break does not have unobstructed exposure to the open ocean.